This invention relates to particulate matter sensors, and particularly to microfabricated particulate matter sensors to measure concentrations of micron-sized particulate matter in the atmosphere.
Airborne particulate matter (“PM”) pollutants are small solid particles or liquid droplets suspended in the atmosphere. These may include, for example, diesel exhaust, tobacco smoke, volcanic ash, and pollen. PM pollutants have diameters ranging from many tens of microns down to a few nanometers. PM pollutants measuring 2.5 microns in diameter or less (PM2.5), or finer particles, are particularly harmful to humans as they may penetrate deep into respiratory systems, and may even get into the bloodstream. In fact, studies show a connection between PM and respiratory and cardiac problems such as aggravated asthma, irregular heartbeat, and premature death in people with reduced heart or lung functionality.
The United States Environmental Protection Agency (“EPA”) sets standards for PM2.5 concentrations in urban air. The EPA has recently reduced its acceptable 24-hour concentration exposure limit for individuals to 35 micrograms/m3. This exposure limit, however, is based on sparse data obtained from large stationary measurement stations. Indeed, existing PM monitors used to measure PM concentration tend to be expensive and have large footprints, rendering them unable to provide detailed measurement information relevant to personal PM exposure at varied locations. While several small-sized PM monitors have recently been developed, these are still too large to allow large-scale deployment as personal PM monitors.
Further, existing PM monitors are generally unable to simultaneously measure multiple PM characteristics, such as PM mass, particle size distributions, chemical composition, and optical properties, to enable accurate identification of PM emissions sources. This identifying information may be used to facilitate strategic targeting of emission reduction approaches, as well as to increase individual awareness of areas or situations likely to aggravate certain medical conditions. Even if this information were currently available, however, it may be inaccurate since existing PM monitors are generally fixed at a few permanent locations.
In view of the foregoing, what are needed are apparatus and methods to reliably measure concentrations of airborne particulate matter at widely varied locations. Further what are needed are apparatus and methods for monitoring airborne particulate matter that are small, inexpensive to manufacture, and easy to carry and utilize. Such apparatus and methods are disclosed and claimed herein.